Material reduction machines such as stump cutting machines are well known. Such machines commonly include a rotating cutter wheel driven by a gas or diesel engine. In the case of a stump cutter, the cutter wheel, while rotating, is advanced toward the stump and moved laterally across the face of the stump. The cutter wheel is mounted at one end of a boom which is, in turn, pivotally mounted on a support frame. Hydraulic boom swing cylinders are used to pivot the boom about the pivot point to move the cutter wheel back and forth across the face of the stump to cut it away. The hydraulic boom swing cylinders are controlled by control lever handles. The handles may also provide an additional function, namely, determining operator presence.
Operator Presence Systems (OPS) are also known in the art. Typically, the systems include two main components: a sensor system activated by an operator when physically located at an operating station, and deactivated when the operator leaves the operating station; and a control system that disables a powered element of the machine when the sensor system is deactivated.
The operator station of a stump cutter often includes three hydraulic control levers that are operated by the individual standing on the ground. In this position, the operator is located in an area where the risk of being struck by a thrown object is minimized. During operation, the entire machine is advanced into the stump, thus requiring the operator to alter his/her standing position to remain comfortably in front of the controls. Job site conditions can also affect how the operator is positioned at the control area. In addition, to avoid fatigue while standing for potentially long periods of time, it is important that the operator be able to comfortably reposition his/her feet and stance. This configuration makes sensing the presence of an operator more difficult than in most machines where the operator is seated wherein operator absence can be detected by measuring the load on the seat.
Sensing the operator's presence at the control levers of a stump cutter is further complicated by the intermittent, and sometimes simultaneous, use of the three control levers. Additionally, operators routinely use gloves for protection from the weather or as protection for an operator's hands. The combined effect results in a situation where the option of utilizing levers with mechanical or electromechanical interlocks is not practical. These devices would require an operator to depress a button or switch while gripping the lever each time the operator moved from one control lever to another. Such a system also provides little freedom in repositioning the operator's hands on the levers. Accordingly, such a system would cause fatigue, result in frequent unwanted cutter wheel stoppages, hinder operation, and create control errors. Freedom of hand/finger position on the control levers is also very important to avoid hand fatigue. Such difficulties are likely to cause operator rejection and provide motivation for circumventing the system.
Therefore, there is a need in the art for an OPS for a stump cutter device that will not inhibit the operator's control of the stump cutter, will provide reliable operation, and can appropriately sense the operator's presence at the control levers without creating fatigue and operator discomfort.
In addition, the material reduction tools on such machines are often heavy and difficult to decelerate due to inertia of the moving tool. Braking systems that have been developed to decelerate the material reduction tool may have less than ideal breaking torque or long term reliability. There is a need in the art to provide a system that includes more effective, more efficient, and more reliable braking over thousands of cycles.